Calculate all circle properties from any known value - radius, diameter, circumference, or area with step-by-step solutions.
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Calculate any circle property from a single known value. Enter radius, diameter, circumference, or area to instantly get all other measurements with step-by-step calculations.
A circle is a perfectly round shape where every point on its boundary is equidistant from the center. The key formulas are: Area = πr², Circumference = 2πr, and Diameter = 2r. Pi (π) is approximately 3.14159.
Circle Area Formula
A = πr²Calculate circular foundations, pipes, and architectural elements.
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Learn circle geometry with visual explanations.
The diameter is exactly twice the radius (d = 2r). Conversely, the radius is half the diameter (r = d/2). The diameter is the longest chord that passes through the center of the circle.
First find the radius from circumference: r = C/(2π). Then use the area formula: A = πr². Our calculator does this automatically when you enter the circumference.
Pi (π) is the ratio of a circle's circumference to its diameter, approximately 3.14159. It's an irrational number that appears in all circle formulas and many areas of mathematics and physics.